If you do it, I'd be interested to hear how it goes.
We've got a 3m long x 2.5 wide quick awning, and as the canvas was custom made, we had them make a triangle piece for the tent end.
The idea was that the triangle would zip onto the awning, with one corner going to the tent buckle for the tropical roof (directly above the breakfast bar pole), and it also had a eyelet and carabiner to hook onto the top of the hatch (carabiner went through the over center latch that holds the hatch down for travel.)
We did it that way so it was quick to put up (no poles, etc), but we've found it's not really worth it.
It's just that something extra to have to setup, it flaps around in the wind, and there's still a gap between the fibreglass and the canvass so you get wet anyway.
If I tired again, I'd probably try to use the existing 'sail track' along the top of the hatch to water proof things a bit better, but I'm not really sure it would be worth the effort, especially as we added the quick awning to avoid having to run the annex though the sail track . . . .